Posted
by
CmdrTaco
on Wednesday October 13, 2010 @11:31AM
from the ishy-science dept.

KentuckyFC writes "The structure of the Milky Way is notoriously difficult to work out because we see our galaxy edge on. That means nearer clouds and stars are superimposed on more distant ones and telling them apart is hard. However, astronomers have unveiled a new map based on velocity measurements made on 870 clouds of carbon monosulphide. This has revealed a number of new features of the Milky Way including a previously unknown spiral arm, some 30,000 light years from the galactic core. But the most surprising finding is that some of our galaxy's spiral arms are straight rather than curved, giving the Milky Way a distinctly square look. That's not quite as outrageous as it sounds. Astronomers know of a number of other galaxies with straight arms, such as the pinwheel galaxy M101. So ours probably looks something like this."

First off, the photo in the article is of the M101 Pinwheel Galaxy, not the Milky Way. Misleading, especially when you have to read all the way down to find out that tidbit and when the title includes 'New Map' we want to see the new map.

No, the article is not describing a barred spiral galaxy. A barred spiral [wikipedia.org] is one where there is a strong bar of stars across the galactic core (and extending well beyond it), and then "normal" spiral arms extend outward (mostly) from the two ends of the bar. The Milkyway is indeed thought to be a barred spiral.

What the article is describing is a spiral galaxy where the spiral arms themselves are straight in parts. And yes these have been observed (as shown in TFA where the Pinwheel galaxy is pictured, notice the lack of a central bar), but no it was not as far as I know theorized that the Milkyway had such a structure until now. Thus, news.

To see the plot, read the paper [arxiv.org] (PDF), not the article. Figure 4 does not look like a square to me. Figure 7 has some squarish shapes drawn over the plot, but it is not highly convincing. Further, these squarish orbits appear in the inner parts of the Galaxy, not the outer shape as one might assume. Orbital shapes change with radius as different gravitational resonances dominate at different distances.

A quick Google search reveals some renderings of the Milky Way, compiling various theories. One of the illustrations has squarish features, but I can't find the "new map" that the article claims was supposedly released.

First, the galaxy doesn't work like the solar system - the orbital velocity of stars doesn't depend strongly on their distance from the centre.

Second, the arms aren't believed to be persistent structures formed from individual stars but density waves that cause increased star formation where they pass. So the arms appear to be very distinct because they have more young, bright stars in them while the space between arms is more older, dimmer stars.

Let's be honest. Slashdot doesn't really have a need for a dedicated "bad analogy guy". There are so many people here who do a great job at it everyday for free. A "bad post guy" is also redundant, for the most part.